The principal focus of this proposal is to investigate the ion transport mechanisms that support fluid transport by the corneal endothelium in terms of solute-solvent coupling and signaling pathways. The project will be carried out in three steps. In the first step, the mechanisms of cell volume regulation in endothelial cells subjected to acute anisosmotic perturbations will be investigated by following changes in cell volume and intracellular ionic activities. The changes in cell volume will be measured using the principles of light scattering, dye dilution and dynamic fluorescence quenching. The indicators for eye dilution technique will include transiently expressed green fluorescent protein or polar fluorescent dyes. In the second step, the modulation of cell volume regulation by signaling pathways involving second messengers and protein kinases will be identified. Finally, the maneuvers of cell signaling that induce profound changes in cell volume regulation will be employed to investigate their influence on fluid transport function by the endothelium in intact corneas. This three-step approach stems from the hypothesis that the ion transport activity and solute-solvent coupling that drive the vectorial fluid transport are mostly identical to those involved during short-term cell volume regulation. The results from this study have directly implications towards the elucidation of the mechanisms underlying fluid transport and their modulation upon long-term contract lens wear, aging, diabetes and intra-ocular surgical maneuvers.